The present invention relates to a sputter deposition process for large area thin film deposition, and more particularly to a magnetron sputtering source having one or more sliding anodes.
Sputter deposition is used in many applications for thin film deposition of various materials on various substrates. Large area coatings for displays, functional coatings (e.g. on architectural glass) or solar cells require a certain uniformity of the film-thickness over the whole substrate area.
Two basic approaches are known for performing sputter deposition. So-called “inline-processing” involves a substrate that is moved alongside a small coating source and is thereby coated with a respective layer. “Single substrate processing” involves coating the entire substrate “at once,” without moving either the source or substrate during deposition. Single substrate processing is normally preferred since it performs the sputter deposition more quickly. This normally requires a coating source that is equal to or larger than the size of the substrate. Such single, large cathodes, however, suffer from an increasing non-uniformity with increasing substrate size due to physical limitations.
For instance, increasing the glass-to-target distance too much can lead to layer problems. On the other hand, if the glass is too close to the targets there will be a lack of electrons in the middle region of the glass, leading to poor layer uniformity.
To get more electrons to the middle of the glass without increasing the glass-to-target distance, greater anode surface area must be provided. To accomplish this, several approaches have been proposed.
One general approach involves providing an array of small cathodes in various orders and arrangements, such as parallel bars, checker-board patterns, and the like. U.S. Pat. No. 6,093,293 to Haag et al., incorporated herein by reference, describes an arrangement of several bar-shaped targets mounted one alongside the other and separated by respective slits. Each of the target arrangements includes a respective electric pad to allow it to be operated electrically independently from the other target arrangement. Further, each target arrangement includes a controlled magnet arrangement generating a time-varying magnetron field upon the target arrangement. Each of the magnet arrangements is controlled independently from the others.
Even such cathode arrays have size limitations, since it is impractical and technically not feasible to raise the number of cathodes arbitrarily with each upscale of the deposition system. Therefore, a further approach for improving sputter deposition uniformity for large substrates is needed.
A major problem with increasing cathode size is a decrease of the electrical field density in the center of the cathode. This decrease results in a lower plasma density and therefor in a lower deposition rate. To avoid this potential drop towards the center of the cathode, it is necessary to provide an anode near the center. Due to limited space between the targets it is not possible to install permanent anodes with sufficient conductivity without raising the danger of arcing during the deposition process.